The present invention relates generally to the electrical, electronic and computer arts, and, more particularly, to semiconductor structures.
Threshold voltage definition is probably one of the most critical parameters in complementary metal-oxide-semiconductor (CMOS) processing technology since it strongly determines the performance of CMOS devices with a given overdrive. In polysilicon/silicon oxynitride (SiON) technology, the threshold voltage was defined by a combination of well/halo/extension doping along with a doping of the gate. As high dielectric constant, or “high-K,” metal gate technology was introduced, the gate doping knob was eliminated and replaced with the use of discrete work function metals, thus making it more challenging to obtain varying threshold voltages for a multitude of devices in a chip.
As semiconductor device scaling progresses, fully-depleted device technology is surfacing. In a fully-depleted device process technology, channel doping is less desired. Moreover, halo doping, which involves embedding ions into a material at the semiconductor surface at an angle that is not normal to the semiconductor surface, is not typically used. This makes threshold voltage definition heavily reliant on gate work function. Typically, technologists are forced to incorporate multiple work function metals to obtain desired threshold voltage devices, thereby making the integration of these various work function metals increasingly more difficult.